This invention relates generally to improvements in gas turbine engines, particularly with respect to improved thermal isolation of engine components from high temperature mainstream combustor gases. More specifically, this invention relates to an improved and effective recirculation pocket for capturing and recirculating any hot gas ingested from a main hot gas flow path into an internally cooled engine cavity, and for recirculating the ingested hot gas to the main flow path.
Gas turbine engines are generally known in the art for use in a wide range of applications such as aircraft engines, auxiliary power units for aircraft, etc. In a typical configuration, the gas turbine engine includes a plurality of sets or rows of stator vanes and rotor blades disposed in an alternating sequence along the axial length of a hot gas flow path of generally annular shape. The rotor blades are mounted at the periphery of one or more rotor disks which are coupled in turn to a main engine shaft. Hot combustion gases are delivered from an engine combustor to the annular hot gas flow path, resulting in rotary driving of the rotor disks to provide an engine output.
In most gas turbine engine applications, it is desirable to regulate the normal operating temperature of certain engine components in order to prevent overheating and potential mechanical failures attributable thereto. That is, while the engine stator vanes and rotor blades are specially designed to function in the high temperature environment of the mainstream hot gas flow path, other engine components such as the rotor disks are not designed to withstand such high temperatures. Accordingly, in many gas turbine engines, the volumetric space disposed radially inwardly or internally from the hot gas flow path, comprises an internal engine cavity through which a cooling air flow is provided. The cooling air flow is normally obtained as a bleed flow from a compressor or compressor stage forming a portion of the gas turbine engine. The thus-cooled internal engine cavity results in maintaining the normal steady state temperature of the rotor disks and other internal engine components at or below a selected temperature.
In the past, relatively high cooling air flows have been required to obtain satisfactory temperature control of engine components within the cooled internal engine cavity. The demand for cooling air has been significantly impacted by the leakage of cooling air from the internal cavity and through the space between adjacent rows of stator vanes and rotor blades, into the hot gas flow path. In addition, the demand for cooling flow has been affected by a somewhat irregular and unpredictable ingestion of mainstream hot gases from the hot gas flow path into the internal engine cavity. Various attempts to prevent flow between adjacent stator vanes and rotor blades have primarily involved the use of overlapping lip-type structures in close running clearance, often referred to as flow discouragers, but these structures have not been satisfactorily effective in preventing hot gas ingestion.
A variety of alternative baffle-type structures and techniques have been proposed, in addition to traditional flow discouragers, in efforts to minimize hot gas ingestion into the internally cooled cavity of a gas turbine engine. Such alternative approaches have included pockets of complex shape, some of which receive separate flows of cooling gas, to prevent hot gas ingestion. In the past, these techniques have been generally ineffective, or have otherwise required structures of complex shape and/or complex mounting arrangements at the time of initial engine production.
The present invention effectively overcomes the problems and disadvantages encountered in the prior art by providing an improved hot gas recirculation pocket in a gas turbine engine to reduce or eliminate hot gas ingestion, wherein the recirculation pocket captures and recirculates ingested hot gas with high efficiency, while additionally being adapted for quick and easy installation during engine production.